1. Field of the Invention
The present invention relates to a method of communicating neighbor base station information to mobile subscriber stations in a mobile communication system.
2. Discussion of the Related Art
In a broadband wireless access system such as a radio mobile Internet system, a mobile subscriber station receives a signal from a neighbor base station and measures a signal quality to find an optimal base station prior to performing handover. If the signal quality of the neighbor base station is superior to that of a serving base station, the mobile subscriber station performs a handover procedure. In doing so, it should be noted that the mobile subscriber station in the radio mobile Internet system performs handover between base stations over an air backbone.
A mobile subscriber station tunes its synchronization with a neighbor base station, receives a signal to measure a signal quality, and previously transmits/receives parameters required for handover to/from a handover target base station. Hence, a quick handover is enabled when handover is substantially performed. Namely, a serving base station periodically transmits information of a neighbor base station to all mobile subscriber stations within the serving base station via a broadcast message. The transmitted information, referred to herein as neighbor base station information, includes, for example, the downlink center frequency, base station identifier(s), and uplink/downlink channel information.
The mobile subscriber station having received the information of the neighbor base stations releases its connection to the serving base station during a specific period, acquires syncs from the neighbor base stations, and then receives signals to measure respective signal qualities.
A handover procedure of a medium access control (MAC) layer according to a related art is explained as follows.
Referring to FIG. 1, illustrating a network topology advertisement, a serving base station delivers information of neighbor base stations to all mobile subscriber stations within the serving base station using a MAC control message. The MAC control message provides physical channel information including uplink/downlink channel information of the neighbor base stations. The mobile subscriber station having received the message can acquire sync with the neighbor base station efficiently.
Referring to FIG. 2, illustrating a neighbor base station scanning process, a serving base station allocates a time for monitoring a neighbor base station to a mobile subscriber station to find a target base station fitting for handover. The allocated time is called a scanning period. During the scanning period, the mobile subscriber station releases its connection to a current serving base station, tunes its sync with a downlink transmission signal of the neighbor base station, and measures a quality of a physical channel. During the scanning period, the serving base station buffers downlink data that will be transferred to the mobile subscriber station. If the scanning period expires, the serving base station transmits the buffered data to the mobile subscriber station. In doing so, by measuring a signal quality transferred from the neighbor base station and by previously exchanging parameters that will be exchanged in handover with a potential handover target base station, a procedure enabling a quick handover in case that a real handover occurs is carried out as well.
Referring to FIG. 3, illustrating a handover initiation process, a signal quality of a neighbor base station is measured. If there exists a neighbor base station having the signal quality superior to that of a serving base station, a procedure for performing a handover is executed. Namely, a mobile subscriber station initiates a handover in a manner of delivering a handover request message to a handover target base station to the serving base station.
However, even though the neighbor base station information provided to the mobile subscriber station by the serving base station is defined in a broadcast control message, the related art method fails to propose how the serving base station acquires the neighbor base station information.